Lecture 20

Question 1

Describe the Jeffress neural coincidence model

Answer 1

some neurons receive input from
both ears and respond to ITD (are essentially
ITD detectors)

Question 2

Describe Reichardt detectors

Answer 2

which
makes a judgment as to whether or not two
incoming signals are received simultaneously
(i.e. have what can be referred to as ‘coincident
detectors’)

Question 3

Describe ITD tuning curves

Answer 3

ITD tuning curves can be examined to see if they provide supporting
evidence for the Jeffress neural coincidence model

• Barn owls have neurons with narrow tuning curves which respond best to
  specifics ITDs

Question 4

Describe how we interpret the numbers on an ITD tuning curve

Answer 4

• μs = microsecond
• 1 second = 1 000 000 μs
• The absolute values on the x axis of this tuning
  curve represents the magnitude of ITD
• 0 = signals that reach both ears at the same time
• Small values = signals that reach each ear with
  less difference in timing
• Large values = signals that reach each ear with
  more difference in timing
• The sign (+ or -) for the values on these tuning
  curves indicates which ear the signal reached first

Question 5

Describe ITD values

Answer 5

The ITD values on these tuning curves are
calculated by subtracting the time at which the
signal reaches the ipsilateral ear from the time at
which the signal reaches the contralateral ear

• Positive values = neurons that respond best to
  sounds that reach the contralateral ear first
• Negative values = neurons that respond best to
  sound that reach the ipsilateral ear first

Question 6

Describe IT tuning curves in animals

Answer 6

• It may be more likely that mammals use population coding to encode ITD for the
  purpose of localizing sounds (whereas birds may use something more like specificity
  coding)

Question 7

Which areas are involved in locating sound?

Answer 7

Area A1 and the posterior belt

Question 8

What does the anterior belt do?

Answer 8

perceiving more complex sound

Question 9

Describe the dorsal stream in hearing

Answer 9

extends from the posterior
belt to the parietal lobe and frontal cortex (red arrows)

• Used to locate sounds

Question 10

Describe the ventral stream in hearing

Answer 10

extends from the anterior
belt to the temporal lobe and frontal cortex (green
arrows)

• Used to identify sounds

Question 11

Describe direct sound

Answer 11

sound that reaches the
listener’s ears straight from the source

Question 12

Describe indirect sound

Answer 12

sound that is reflected off
of environmental surfaces and then to the
listener

Question 13

Describe the precedence effect

Answer 13

When sound comes from the lead speaker followed by the lag
speaker with a long delay, listeners hear two sounds

• When the delay is decreased to 5-20 msec, listeners hear the
  sound as only coming from the lead speaker

Question 14

define architectural acoustics

Answer 14

the study of how sounds are reflected in
rooms (e.g. how the design of concert halls influence the perception of sound)

Question 15

Define reverberation time

Answer 15

the time it takes sound to decrease to 1/1000th of its
original pressure

• If it is too long, sounds seem ‘muddled’
• If it is too short, sounds seem ‘dead’
• Ideal times are around two seconds

Question 16

Describe intimacy time

Answer 16

time between when sound leaves its source and when the first
reflection arrives

• Best time is around 20 ms

Question 17

Describe bass ratio

Answer 17

ratio of low to middle frequencies reflected from surfaces

• High bass ratios are best

Question 18

Describe spaciousness factor

Answer 18

fraction of all the sound received by listener that is indirect

• High spaciousness factors are typically perceived as most pleasing

Question 19

Describe the auditory scene

Answer 19

the array of all sound
sources in the environment

Question 20

Describe auditory scene analysis

Answer 20

process by
which sound sources in the auditory scene
are separated into individual perceptions

• Does not happen at the cochlea since
  simultaneous sounds are processed
  together in the pattern of vibration of the
  basilar membrane

Question 21

Describe simultaneous grouping

Answer 21

Heuristics help to perceptually organize stimuli (similar to idea of Gestalt
principles for grouping objects based visual properties)

• Onset time: sounds that start at different times are likely to come from different
  sources
• Location: a single sound source tends to come from one location
• Individual sources of sound also tend to move in a smooth and continuous
  way (e.g. a car driving by)
• Similarity of timbre and pitch: similar sounds are grouped together (e.g. a flute
  will typically continue sounding like a flute throughout an entire piece of music)

Question 22

Describe sequential grouping

Answer 22

When a single instrument alternates rapidly between streams of low and high
notes, the listener perceives it as two separate melodies
* This is referred to as implied polyphony or compound melodic lines by
musicians, or auditory stream segregation by psychologists

Question 23

Describe the scale illusion

Answer 23

Experiment by Deutsch (1975): demonstrates
the scale illusion or melodic channeling

• Stimuli were two sequences alternating
  between the right and left ears
• Listeners perceive two smooth sequences by
  grouping the sounds by similarity in pitch
• Because sounds with the same frequency
  usually come from the same source in the
  natural environment, this heuristic often allows
  us to accurately separate sound sources

Question 24

Describe proximity in time

Answer 24

sounds that occur in rapid succession usually come from the same source

• This principle was illustrated in auditory streaming

Question 25

Define auditory continuity

Answer 25

sounds that stay constant or change smoothly are
usually from the same source

Question 26

Describe auditory continuity study

Answer 26

In the silence condition,
listeners perceived that the
sound stopped during the
gaps
* In the noise condition, the
perception was that the sound
continued behind the noise
* Similar to Gestalt principle of
good continuation

Question 27

Describe Deustch study

Answer 27

Melody is played with notes alternating between octaves (e.g. “Three Blind
Mice”)
* Listeners find it difficult to identify the song in a control condition in which that
is all they hear
* If they are first primed with hearing a more ‘typical’ (i.e. within the same
octave) version of that melody, they can then hear it in the modified version
* Demonstrates the role of experience and memory, and in particular melody
schema, in interpreting melodies

Question 28

Describe ventriloquist effect

Answer 28

Visual capture (aka the ventriloquist effect) occurs when an observer
incorrectly perceives a sound as coming from a location suggested by visual
information
* Represents an example of vision ‘superseding’ audition

Question 29

Describe two flash illusion

Answer 29

• In the two-flash illusion, seeing a
  single dot flash on a screen is
  misinterpreted as two flashed dots if
  accompanied by two beeps
• Represents an example of audition
  ‘superseding’ visual input

Question 30

Describe coordinated receptive fields

Answer 30

Coordinated receptive fields refer to
neurons which respond to multimodal
stimuli (e.g. sound and vision) that
originate in common regions of space

Question 31

Describe Thaler study results

Answer 31

used expert blind echolocators to create clicking sounds

• These stimuli activated visual cortex in the blind participants, but not the controls
  (with normal vision)